To visually test vague.nvim, I use git repos in different languages ranging from zig to javascript to see how the colorscheme looks in the context of each language.
These git repos are just random project that came up first on a google search.
Here are the languages I use to visually test the theme. If they have a repository, they deserve to be credited in some way shape or form, if it says N/A, that means either I made it, or it's just 1 file.